1. Field of the Invention
The present invention relates to a multi-plate clutch.
2. Discussion of the Background
In an exemplar conventional clutch, the rotational driving force of a crankshaft is transmitted to a transmission shaft by making plural clutch discs clamped with the biasing force of a disc spring so as to be brought into contact with one another. The exemplar conventional clutch is equipped with a cam mechanism to assist the clamping force. When the rotational driving force from the crankshaft increases, the cam mechanism generates a force in such a direction as to clamp the clutch discs together. The force thus generated is added to the clamping force generated by the disc spring, so that the total clamping force acting on the clutch discs is increased (see, Japanese Patent Application Publication No. 2008-38954, for example, FIG. 1 of the Japanese publication).
With the above-mentioned configuration, as the rotational driving force from the crankshaft increases, the clamping force the cam mechanism adds also increases. For this reason, a clamping force that is larger than necessary may be generated in some conditions of the vehicle. In order to secure high stiffness of the component parts of the clutch against such a large clamping force, the clutch mechanism is required to have heavyweight and large size.